Curable composition comprising elastomeric terpolymer of carbon monoxide

ABSTRACT

Terpolymers having 1,4-diketo functionalities and a carbonyl group concentration of about 5-20% of polymer weight can be conveniently cured by heating with an aromatic primary diamine or its precursor and a catalytic amount of an acid having a pKa of at most about 3. Cured polymers have good physical properties and are suitable in such applications as, for example hose, tubing, wire coatings, gaskets, and seals.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of my application Ser. No. 472.752, filedMar. 7, 1983.

BACKGROUND OF THE INVENTION

This invention relates to certain novel curing systems for copolymers ofethylene with carbon monoxide as well as to curable compositionscomprising such copolymers together with a curing system of the typedisclosed hereafter and to cured polymers obtained by heating the abovecurable compositions to their cure temperature.

Dipolymers of carbon monoxide with ethylene and terpolymers withethylene and another ethylenically unsaturated monomer such as, forexample, methyl acrylate, or vinyl acetate are well known. Suchcopolymers are known to contain 1,4-diketo functions arising fromCO/unsaturated monomer/CO triads. Although such polymers can be cured byknown free radical techniques, for example, in the presence ofperoxides, free radical curing suffers from various shortcomings. Thus,for example, because of the inherently non-discriminating nature ofperoxide cures, various customary additives, which could be adverselyaffected by the peroxide (for example, certain fillers, andplasticizers), cannot be used. Furthermore, peroxides have a deleteriouseffect on commonly used antioxidants and processing oils.

It is, therefore, desirable to have available a non-peroxide curingsystem for ethylene/carbon monoxide copolymers.

SUMMARY OF THE INVENTION

According to this invention, there is provided a curing system forelastomeric terpolymers of ethylene with another ethylenicallyunsaturated monomer and carbon monoxide, in which the ketone carbonylconcentration is about 5-20 weight percent of the polymer, said curingsystem consisting essentially of about 0.15 to 8.0 mole % of an aromaticprimary diamine based on the ketone carbonyl groups of the terpolymer orof a precursor which will liberate a free aromatic primary diamine underthe cure conditions, and a catalytic amount of an acid having a pKa ofat most about 3 or a precursor capable of liberating such acid under thecure conditions.

There also are provided curable polymer compositions comprising aterpolymer of ethylene with another ethylenically unsaturated monomerand with carbon monoxide and the above diamine/acid curing system.

Finally, there also is provided a process for curing polymers by heatingthe above curable compositions to a temperature at which curing takesplace.

BRIEF DESCRIPTION OF THE DRAWING

The drawing is a proton nuclear magnetic resonance (nmr) spectrum of anethylene/methyl acrylate/carbon monoxide terpolymer wherein specifictypes of protons are correlated with polymer structural units.

DETAILED DESCRIPTION OF THE INVENTION

Unless the CO group content is at least about 5% of the copolymerweight, the statistical distribution of CO groups throughout themolecule may result in a number of CO/ethylenic monomer/CO triads whichis too small for effective crosslinking. The preferred ketone CO groupconcentration is 8-12 weight percent of the polymer weight. A typicalterpolymer which can be successfully cured according to the process ofthe present invention contains about 35% of ethylene, 55% of methylacrylate, and 10% of carbon monoxide. High CO group concentrations,above about 20 weight percent, result in stiff, nonelastomeric curedpolymers. For the purpose of this disclosure, an elastomer is defined asa polymer which, when stretched to twice its length and released, atroom temperature, returns with force to its original length.

The carbon monoxide concentration of ethylene/unsaturated monomer/carbonmonoxide terpolymers can be determined by nuclear magnetic resonance(nmr) analysis. Pertinent structural assignments are as follows:

For CH₃ of methyl acrylate δ=3.59 ppm. For ethylene CH₂ in α-position toCO in 1:1 ethylene/CO structural units δ=3.00-2.40 ppm.

For CH₂ in α-position to CO in other structural units and for CH of##STR1## where R' and R" are alkyl groups δ=2.40-2.00 ppm. For CH₂ inβ-position to CO δ=1.55 ppm.

Those terpolymers normally fall in the following structural types:##STR2##

where E stands for the ethylene group, and R stands for an alkyl group.The starred groups are those containing protons used in thecalculations.

The amount of ethylenically unsaturated monomer X in E/X/CO terpolymersis calculated from the areas of the nmr peaks corresponding to thestarred groups. Corrections for other protons associated with monomer Xcan then be made in the spectrum.

The monomer composition of an ethylene/methyl acrylate/carbon monoxideterpolymer is calculated as shown below to illustrate the practicalapplication of the nmr method. In the following discussion MA stands formethyl acrylate. Circled numbers correspond to those shown in thedrawing.

Regardless of its environment, the MA methyl has one resonance (line ○1) at 3.59 ppm. ##EQU1## α-methylenes of E/CO in 1,4 dione or 1:1 units,lines ○2 and ○3 . ##EQU2## α-methylenes of E/CO in (2 or more):1 units,line ○4 . ##EQU3## All the remaining lines ○5 , ○6 , ○7 ##EQU4##

Carbon monoxide

B+C=F the number of units due to one mole of CO.

Total ethylene ##EQU5## Analysis of similar CO-containing terpolymers bynmr spectroscopy is discussed, for example, in Chapter 4 (J. E. McGrathet al) of Applications of Polymer Spectroscopy, edited by E. G. Brame,Jr., Academic Press, New York, 1978, pp. 42-55.

Typical copolymerizable ethylenically unsaturated monomers X in theterpolymers include, α,β-unsaturated C₃ -C₂₀ mono- and dicarboxylicacids, vinyl esters of saturated C₁ -C₁₈ carboxylic acids, alkyl estersof α,β-unsaturated C₃ -C₂₀ mono- and dicarboxylic acids, vinyl C₁ -C₁₈alkyl ethers, acrylonitrile, methacrylonitrile, copolymerizableunsaturated hydrocarbons such as C₃ -C₁₂ α-olefins, cyclic hydrocarbonssuch as norbornene, and vinyl aromatic compounds such as styrene.

The reaction of 1,4-diketo groups with primary aromatic amines isbelieved to result in the formation of a stable pyrrole structure, asshown in the equation below: ##STR3## wherein R stands for an aromaticdivalent organic radical, and the wavy lines represent polymer chains.

The primary aromatic diamine, H₂ N--R--NH₂ can be any diamine, includingdiamines in which R contains heteroatoms, such as, for example, N, S, orO. Suitable diamines include, for example, p,p'-methylenedianiline,p-phenylenediamine, p,p'-oxydianiline, p-toluidine, and2,4-toluenediamine. Polymers cured with such diamines have very goodthermal and hydrolytic stability. Methylenebis(o-chloroaniline) also canbe used, although this chemical has been designated as a potentialcarcinogen and is no longer commercially available from the Du PontCompany; it is still available, however, from other manufacturers.

Free diamines may react quite fast with 1,4-diketo copolymers andtherefore form scorchy compositions. The most suitable diaminecomponents of the compositions of the present invention are blockeddiamines, which decompose under the cure conditions, thus releasing thefree diamine in situ. A typical blocking group is the carbamate. Blockeddiamines provide excellent processing safety. Aliphatic diamines arevery scorchy, even in precursor form, such as, for example,hexamethylenediamine carbamate. Further, reactions with aliphaticdiamines appear to be reversible. For these reasons, aliphatic diaminesare not suitable in the compositions of the present invention.

For the purpose of the present disclosure, the term "aromatic" meansthat there is present at least one cyclic structure having a system ofconjugated double bonds, as, e.g., in benzene or naphthalene.

The diamine or diamine precursor concentration is fairly critical inthat effective crosslinking will not be obtained below the lower limitof the above recited range, while above the upper limit reaction of thecure sites (1,4-diketo groups) with one amine group of the diamine willresult in a polymer containing amine-terminated pendant groups, ratherthan in a crosslinked polymer.

The crosslinking reaction according to the present invention iscatalyzed by acids, which may be inorganic or organic, so long as theirpKa is no more than about 3. In addition to normal inorganic acids suchas, for example, sulfuric, phosphorous, phosphoric, or hydrochloric,various organophosphonous and organophosphonic acids, sulfonic acids,chloroacetic acids, salicylic acid, and malonic acid are suitablecatalysts. It is practical to use acid precursors, which form the freeacids under cure conditions, thus further increasing the processingsafety of the compositions of this invention. Typical such precursorsare, for example various acid esters, which decompose to liberate theacids. Such precursors include various alkyl tosylates, which are knownto undergo pyrolysis to p-toluenesulfonic acid (pKa=0.70) and thecorresponding alkene, as shown below: ##STR4##

A commercial antioxidant, tri(mixed mono- and dinonyl phenyl)phosphite,sold by Uniroyal under the name "Polygard", proved to be an effectivecure catalyst. This material is known to slowly hydrolyze in thepresence of moisture to liberate phosphorous acid, which always ispresent in a small amount in the commercial material. The pKa is about2. A sample of "Polygard" was found to contain about 1.1 weight percent(0.013 mole/100 g) of phosphorous acid.

The maximum cure rates are obtained when the molar ratio of the acidcatalyst to the diamine curing agent is close to 0.1. Acceptable ratesare still obtained when this ratio is as low as 0.03 or as high as 1. Nosignificant improvement can be expected above that latter ratio, while alarge amount of a strong acid could cause polymer degradation.

The use of blocked diamine or polyamine curing agent and/or blocked acidcatalyst (that is, precursors of the diamine or polyamine and of theacid) improves the processing safety of the polymer compound. The curetemperature preferably should be the same for the curing system of thepresent invention as normally is employed for polymer cures, so that noequipment or operating procedure modifications will be required. Theusual industrial cure temperature of about 177° C. is suitable in thepresent process. Naturally, when a protected curing agent or acidcatalyst is employed, it must be so chosen that its thermaldecomposition to the free amine and/or free acid occurs at the curetemperature at a satisfactory rate.

Polymer compounds containing the curing agent and acid catalyst areprepared by standard mixing techniques, for example, in a rubber mill oran internal mixer.

Curing carbonyl group-containing terpolymers according to this inventiongives products which have good physical properties and are suitable insuch applications as, for example, hose, tubing, wire coating, gaskets,seals, coated fabrics, and sheet goods.

This invention is now illustrated by examples of certain preferredembodiments thereof, where all parts, proportions, and percentages areby weight unless indicated otherwise, except that curing agent andcatalyst concentrations are also expressed as mole % based on ketonecarbonyl groups. For methylenedianiline complexes with alkali metalchlorides the mole % concentration is calculated on the basis of freemethylenedianiline. The abbreviation "phr" means "parts per 100 parts ofpolymer". All the cured polymeric compositions of this invention wereelastomeric.

EXAMPLE 1 Polymer Preparation

An ethylene/methyl acrylate/carbon monoxide (E/MA/CO) 35/55/10terpolymer is prepared according to the general processes of U.S. Pat.Nos. 2,495,286 to Brubaker and 3,780,140 to Hammer in a continuous,stirred, high pressure 725 mL polymerization reactor at 190° C. and 186MPa. In a typical run, the feed stream compositions, flow rates andpolymer composition are as follows:

    ______________________________________                                        Feed       Composition (parts)                                                                            Rate, (kg/hr)                                     ______________________________________                                        Ethylene   ethylene (100)   6.36                                              Comonomer 1                                                                              methyl acrylate (100)                                                                          1.19.sup.1                                                   monoethyl ether                                                               of hydroquinone (100 ppm)                                                     2,6-di-t-butyl-                                                               4-methyl phenol (220 ppm)                                          Comonomer 2                                                                              CO (100)         0.30                                              Solvent    methanol (25)    0.27.sup.2                                                   t-butyl alcohol (75)                                               Catalyst   2-t-butylazo-2-  0.5.sup.3                                         Solution   cyano-4-methoxy-                                                              methylpentane (1512 ppm)                                                      methanol (25)                                                                 t-butyl alcohol (75)                                               Telogen    acetone (100)    0.45                                              ______________________________________                                         .sup.1 Total Comonomer 1 composition feed rate                                .sup.2 Total solvent feed rate                                                .sup.3 Total catalyst solution feed rate                                 

Other E/MA/CO polymer compositions are prepared by variations in thereaction paramters such as comonomer solution composition, relative feedrates of the monomer streams, temperature, pressure, and monomerconversion.

EXAMPLE 2 Curing of an E/MA/CO terpolymer with a complex ofmethylenedianiline with lithium chloride

A terpolymer having a composition of 53% E, 37% MA, and 10% CO, 100parts, was compounded on a water-cooled, two-roll rubber mill with 50parts of SRF (N774) carbon black, 1 part of substituted diphenylamineantioxidant ("Naugard" 445, Uniroyal), 1 part tri(mixed mono- anddinonyl phenyl)phosphite ("Polygard", Uniroyal) and various quantitiesof lithium chloride complex of methylenedianiline. (MDA)₃ LiCl.

Slabs for specimens for the determination of tensile properties andpellets for compression set measurements were cured in presses at about4.5 MPa pressure and 177° C. Molds were loaded and unloaded hot. Thestress-strain properties--M₁₀₀ (100% modulus), M₂₀₀ (200% modulus),T_(B) (tensile strength at break), and E_(B) (percent elongation atbreak)-were measured by ASTM method D-412. Compression set (Comp. Set B)of the cured pellets was measured by ASTM method D-395.

Table I shows the results obtained with press cures of 30 minutes and 60minutes with several concentrations of the curing agent. The acidcatalyst required for the crosslinking reaction is supplied by the acidimpurities known to be present in the "Polygard" antioxidant. Theomission of "Polygard" in these stocks without the inclusion of someother acid catalyst fails to produce a vulcanized polymer under the samepress cure conditions.

                  TABLE I                                                         ______________________________________                                        VULCANIZATE PROPERTIES OF (MDA).sub.3 LiCl-CURED                              E/MA/CO TERPOLYMER*                                                                      Cure Time                                                                     60 min      30 min                                                            A     B         C       D                                          ______________________________________                                        (MDA).sub.3 LiCl, phr                                                                      1.22    2.01      2.80  1.50                                     mole %       1.64    2.69      3.72  2.08                                     M.sub.100 (MPa)                                                                            2.8     6.8       9.0   7.5                                      M.sub.200 (MPa)                                                                            9.1     --        --    --                                       T.sub.B (MPa)                                                                              15.5    13.6      15.2  15.9                                     E.sub.B (%)  290     160       145   190                                      Shore A, Hardness                                                                          55      60        66    57                                       Compression Set B                                                                          23      26        29    12                                       70 hr/100° C.                                                          Compression Set B                                                                          34      30        32    24                                       70 hr/150° C.                                                          ______________________________________                                         *Recipe:                                                                      E/MA/CO terpolymer (100)                                                      Carbon Black (50)                                                             "Polygard" (1)                                                                "Naugard" 445 (1)                                                             (MDA).sub.3 LiCl (as shown)                                              

EXAMPLE 3 Vulcanizate properties of E/MA/CO terpolymers cured with(MDA)₃ LiCl complex

Four E/MA/CO terpolymers having different proportions of monomers wereindividually compounded as described in Example 1. Table II shows theproperties of vulcanizates obtained after a one-hour cure at 177° C.followed by a post-cure of four hours at 150° C. As in Example 2,"Polygard" functions as the required acid catalyst.

                  TABLE II                                                        ______________________________________                                        VULCANIZATE PROPERTIES OF (MDA).sub.3 LiCl-CURED                              E/MA/CO TERPOLYMER                                                                       A     B         C       D                                          ______________________________________                                        Polymer*     100     100       100   100                                      (MDA).sub.3 LiCl, phr                                                                      2.6     2.6       2.6   2.6                                      mole %       5.0     4.5       4.2   3.9                                      M.sub.100 (MPa)                                                                            5.0     6.6       7.1   6.6                                      M.sub.200 (MPa)                                                                            16.0    19.0      --    19.1                                     T.sub.B (MPa)                                                                              17.9    20.3      20.3  20.5                                     E.sub.B (%)  207     203       200   203                                      ______________________________________                                         *A -- 43.8% E/49.1% MA/7.1% CO                                                B -- 41.0% E/51.2% MA/7.8% CO                                                 C -- 37.6% E/53.9% MA/8.5% CO                                                 D -- 38.1% E/53.0% MA/8.9% CO                                            

EXAMPLE 4

Stocks were compounded on a water-cooled, two-roll rubber mill.Oscillating Disk Rheometer (ODR) measurements were obtained on theuncured stocks at 177° C. by ASTM Method D-2705. The cure rates weredetermined by measuring the maximum slope of the ODR traces.

Table III shows cure rates obtained with the following diamines;methylenedianiline, methylenedianiline-sodium chloride complex,p-phenylenediamine, m-phenylenediamine, 4-aminophenyl ether and4,4'-diaminodiphenyl disulfide as curing agents with "Polygard"functioning as the required acid catalyst. In stocks B, C, E, F, and Gcyclohexyl tosylate also was added as a precursor of p-toluenesulfonicacid.

The ODR data for stock A compared with stocks B and C, and similarlystock D compared with E clearly demonstrate the very large rateenhancements, evidenced by increases of maximum slope, obtained by theinclusion of this additional acid catalyst.

                                      TABLE III                                   __________________________________________________________________________                 A   B   C   D   E   F   G   H   I                                __________________________________________________________________________    Polymer (1)* 100 100 100 100 100 100 100                                      Polymer (2)**                            100 100                              SRF (N774) Carbon                                                                          50  50  50  50  50  50  50  50  50                               Black                                                                         "Naugard" 445                                                                              1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                              Curing agent                                                                  MDA, phr     1.25                                                                              1.25                                                                              1.50                                                     mole %       1.84                                                                              1.84                                                                              2.22                                                     (MDA).sub.3 NaCl, phr    2.00                                                                              2.00                                             mole %                   2.67                                                                              2.67                                             p-phenylenediamine, phr          1.09                                         mole %                           2.9                                          m-phenylenediamine, phr              1.09                                     mole %                               2.9                                      4-aminophenyl ether, phr                 1.49                                 mole %                                   2.6                                  4,4'-diaminodiphenyl                                                          disulfide,                                                                    phr                                          1.87                             mole %                                       2.6                              Acid Catalyst                                                                 "Polygard", phr                                                                            1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0                              cyclohexyl tosylate, phr                                                                       1.20                                                                              0.96    1.20                                                                              0.20                                                                              0.20                                     mole %           1.34                                                                              1.67    1.34                                                                              0.23                                                                              0.23                                     ODR at 177° C.                                                         Minimum torque, N · m                                                             0.15                                                                              0.23                                                                              0.41                                                                              0.42                                                                              0.38                                                                              0.43                                                                              0.50                                                                              0.25                                                                              0.38                             Maximum torque (at                                                                         3.45                                                                              5.68                                                                              5.06                                                                              5.14                                                                              6.10                                                                              5.65                                                                              5.50                                                                              2.99                                                                              1.83                             60 minutes), N · m                                                   Maximum slope,                                                                             0.48                                                                              2.85                                                                              1.93                                                                              0.62                                                                              2.09                                                                              1.16                                                                              0.98                                                                              0.24                                                                              0.11                             N · m/min                                                            __________________________________________________________________________     *Polymer (1) -- 52.8% E/37.3% MA/9.9% CO                                      **Polymer (2) -- 54.5% E/37.5% MA/8.0% CO                                

EXAMPLE 5 Evaluation of acid catalysts

Stocks were compounded as shown in Table IV. Cure rates at 177° C. weremeasured as in Example 13. Acid strength is given as pKa at 25° C. inwater. The data in Table IV show the cure rates obtained with thelithium chloride complex of methylenedianiline as the curing agent anddifferent acid catalysts. The (MDA) LiCL complex was used in all runs atthe level of 1.59 phr (2.9 mole %). It will be noted that the cure ratesincrease with acid strength. For example, in the presence of2,6-dihydroxybenzoic acid (pKa=1.22) the cure is 6.8 times faster thanin the presence of 2,4-dihydroxybenzoic acid (pKa=3.29). Acids with pKain range of 4 to 5 give low rates of cure, while acids with pKa in therange of 2.5 to 3.0 give moderate rates of cure, and acids with pKa ofless than 2.0 give fast rates of cure.

                                      TABLE IV                                    __________________________________________________________________________                    A   B   C   D   E   F   G   H   I                             __________________________________________________________________________    Polymer (1)*    100 100                     100 100                           Polymer (2)**           100 100 100 100 100                                   SRF (N774) Carbon                                                                             50  50  50  50  50  50  50  50  50                            Black                                                                         (MDA).sub.3 LiCl, phr                                                                         1.59                                                                              1.59                                                                              1.59                                                                              1.59                                                                              1.59                                                                              1.59                                                                              1.59                                                                              1.59                                                                              1.59                          mole %          2.87                                                                              2.87                                                                              2.87                                                                              2.87                                                                              2.87                                                                              2.33                                                                              2.33                                                                              2.87                                                                              2.87                          Acid Catalyst (pKa)                                                           Trimethylacetic acid                                                          (5.03), phr     0.42                                                          mole %          1.60                                                          Benzoic Acid (4.19), phr                                                                          0.50                                                      mole %              1.60                                                      Diethylmalonic acid                                                           (3.15), phr             0.22                                                  mole %                  0.53                                                  Cyanoacetic acid (2.45), phr                                                                              0.14                                              mole %                      0.63                                              2,4-Dihydroxybenzoic acid                                                     (3.29), phr                     2.20                                          mole %                          0.49                                          2,5-Dihydroxybenzoic acid                                                     (Unknown but believed                                                         to be about 3.3), phr               0.20                                      mole %                              0.49                                      2,6-Dihydroxybenzoic acid                                                     (1.22), phr                             0.20                                  mole %                                  0.49                                  p-Methoxyphenylphosphonic acid                                                (< 2), phr                                  0.78                              mole %                                      1.35                              p-Methoxyphenylphosphinic acid                                                (<2), phr                                       0.72                          mole %                                          1.35                          ODR at 177° C.                                                         Minimum torque, N · m                                                                0.17                                                                              0.23                                                                              0.28                                                                              0.53                                                                              0.15                                                                              0.18                                                                              0.51                                                                              0.28                                                                              0.45                          Maximum torque (at                                                                            0.90                                                                              2.30                                                                              2.00                                                                              3.16                                                                              1.56                                                                              2.97                                                                              3.49                                                                              4.60                                                                              4.40                          60 minutes), N · m                                                   Maximum slope,  0.03                                                                              0.06                                                                              0.289                                                                             0.41                                                                              0.108                                                                             0.194                                                                             0.739                                                                             1.06                                                                              1.14                          N · m/min                                                            __________________________________________________________________________     *Polymer (1) -- 38.4% E/54.3% MA/7.3% CO                                      **Polymer (2) -- 36.2% E/54.8% MA/9.0% CO                                

EXAMPLE 6

An E/MA/CO 38.4/54.3/7.3% terpolymer, 100 parts, was compounded by thetechnique used in the previous examples with 50 parts of SRF (N-774)carbon black and 1.5 parts (2.87 mole %) of methylenedianiline (MDA) asthe curing agent. Cyclohexyl tosylate was the acid catalyst, but itsconcentration, based on 100 parts of the compounded rubber, was variedas shown in Table V.

The data presented in Table V show that cyclohexyl tosylate inconcentrations as low as 0.06 part is an effective accelerator for theMDA cure of this E/MA/CO terpolymer, and that very fast rates areobtained with concentrations above 0.15 part.

                  TABLE V                                                         ______________________________________                                                     A    B      C      D    E    F                                   ______________________________________                                        Compounded Rubber                                                                            100    100    100  100  100  100                               Cyclohexyl                                                                    Tosylate,                                                                     phr            1.19   0.90   0.60 0.30 0.15 0.06                              mole %         1.8    1.4    0.9  0.5  0.2  0.1                               ODR at 177° C.                                                         Minimum torque, N · m                                                               0.09   0.10   0.11 0.12 0.08 0.11                              Maximum torque (at                                                                           4.84   4.63   4.60 4.52 4.30 4.70                              60 minutes), N · m                                                   Maximum slope, 1.12   1.12   1.01 1.01 0.70 0.28                              N · m/min                                                            ______________________________________                                         Recipe:                                                                       Polymer E, 38.4%/MA, 54.3%/CO, 7.3% (100 parts)                               SRF (N774) Carbon Black (50 parts)                                            Methylenedianiline (1.5 parts, 2.87 mole %)                                   Cyclohexyl tosylate (as shown)                                           

EXAMPLE 7

An E, 36.2%/MA, 54.8%/CO, 9.0% terpolymer was compounded as shown inTable VI. The concentration of methylenedianiline, which was the curingagent, was varied.

The ODR data in Table VI show that both the cure rate (evidenced bychanges in maximum slope) and the state of cure (evidenced by changes inmaximum torque) rise through a maximum and then decrease as a functionof methylenedianiline concentration, and that this maximum occurs at adiamine concentration of 0.01 mole/100 g of polymer. It is well knownthat this type behavior is indicative of systems in which the polymercontains a limited cure site concentration. For the above example thisdata indicates a cure site concentration of 0.02 mole/100 g of polymer.The cure sites are attributed to 1,4-diketone functionalities that arisefrom CO/ethylene/CO triads in the polymer chain.

                                      TABLE VI                                    __________________________________________________________________________                    A   B   C   D   E   F   G   H                                 __________________________________________________________________________    Polymer*        100 100 100 100 100 100 100 100                               SRF (N-774)     50  50  50  50  50  50  50  50                                Carbon Black                                                                  Cyclohexyl Tosylate, phr                                                                      0.33                                                                              0.33                                                                              0.33                                                                              0.33                                                                              0.33                                                                              0.33                                                                              0.33                                                                              0.33                              mole %          0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                                                                              0.40                              Methylenedianiline (MDA), phr                                                                 0.39                                                                              0.78                                                                              1.19                                                                              1.58                                                                              1.97                                                                              2.36                                                                              3.13                                                                              3.94                              mole %          0.6 1.2 2.0 2.5 3.1 3.8 5.0 6.3                               ODR at 177° C.                                                         Minimum torque, N · m                                                                0.24                                                                              0.31                                                                              0.34                                                                              0.34                                                                              0.28                                                                              0.32                                                                              0.29                                                                              0.29                              Maximum torque (at                                                                            1.42                                                                              2.49                                                                              3.51                                                                              4.55                                                                              3.29                                                                              5.46                                                                              5.38                                                                              4.52                              60 minutes, N · m                                                    Maximum slope, N · m/min                                                             0.42                                                                              0.86                                                                              1.01                                                                              1.01                                                                              0.99                                                                              0.90                                                                              0.75                                                                              0.45                              __________________________________________________________________________     *Polymer -- 36.2% E/54.8% MA/9.0% CO                                     

I claim:
 1. A curable composition comprising an elastomeric terpolymerof ethylene with carbon monoxide and with another ethylenicallyunsaturated monomer, in which ketone carbonyl concentration is about5-20% of the polymer weight and a curing system for said polymerconsisting essentially of about 0.15 to 8.0 mole % of an aromaticprimary diamine based on the ketone carbonyl groups or an equivalentamount of a precursor which will liberate free diamine under the cureconditions, and a catalytic amount of an acid having a pKa of at mostabout 3 or a precursor capable of liberating an equivalent amount ofsuch acid under the cure conditions.
 2. A composition of claim 1 whereinthe ketone carbonyl group concentration is 8-12% of the polymer weight.3. A composition of claim 1 wherein the polymer is a terpolymer ofethylene with carbon monoxide and a monomer selected from the groupconsisting of α,β-unsaturated C₃ -C₂₀ mono- and dicarboxylic acids,vinyl esters of saturated C₁ -C₁₈ carboxylic acids, alkyl esters ofα,β-unsaturated C₃ -C₂₀ mono- and dicarboxylic acids, vinyl C₁ -C₁₈alkyl esters, acrylonitrile, methacrylonitrile, and copolymerizableunsaturated hydrocarbons.
 4. A composition of claim 2 wherein thecopolymerizable hydrocarbons are C₃ -C₁₂ α-olefins, norbornene, orvinylaromatic compounds.
 5. A composition of claim 3 wherein the polymeris an ethylene/methyl acrylate/carbon monoxide terpolymer.
 6. Acomposition of claim 1 wherein the molar ratio of the acid to thediamine is 0.03 to
 1. 7. A composition of claim 5 wherein the molarratio of the acid to the diamine is about 0.1.
 8. A composition of claim1 wherein a diamine precursor is present as its carbamate.
 9. Acomposition of claim 1 wherein the acid catalyst is phosphorous acid ora mixture of phosphorous acid with a phosphite ester.
 10. A compositionof claim 1 wherein the acid catalyst is an alkyl tosylate.
 11. A curedpolymer obtained by heating a composition of claim 1 to a temperature atwhich cure takes place.
 12. A cured polymer obtained by heating acomposition of claim 3 to a temperature at which cure takes place.
 13. Acomposition of claim 1 wherein the primary diamine present in the curingsystem is present in the form of a complex with an alkali metal halide.14. A composition of claim 13, wherein the primary diamine isp,p'-methylenedianiline.